1. Field of the Invention
The present invention relates to an image display device represented by a CRT (Cathode-Ray Tube) display device; particularly, relates to improving the visual quality of displayed image.
2. Description of the Background Art
FIG. 25 is a block diagram showing an internal structure of a conventional image display device as a background of the present invention. This device 150 is formed as a CRT device having a CRT 91. An image signal Pin inputted from the exterior is amplified by an amplifier 92 into an image signal Pc. The image signal Pc is supplied to the cathode (not shown) of the CRT 91. The input of the amplifier 92 is connected to a parallel circuit of a resistor 93 and a series circuit. The series circuit includes a capacitor 94 and a resistor 95 connected in series to each other. The input and the output of the amplifier 92 are connected to each other through a resistor 96. Thus, the device 150 comprises an active type (a current feedback type) of a video amplifying circuit.
A series circuit having an inductor 97 and a resistor 98 connected in series to each other is interposed into a path between the output of the amplifier 92 and the cathode of the CRT 91. The gain of the video amplifying circuit including the amplifier 92 is defined by resistance of the resistors 93, 95, 96 and 98, capacitance of the capacitor 94, and an inductance of the inductor 97. In particular, the capacitor 94 and the inductor 97 can compensate a high frequency component of the gain. That is, the capacitance of the capacitor 94 and the inductance of the inductor 97 define a frequency characteristic of the gain.
The CRT 91 is further connected to a high voltage generation unit 99. The high voltage generation unit 99 supplies the CRT 91 with high voltage so as to implement an injection of electron beam inside the CRT 91. As the conventional device 150 is so formed as described above, an image represented by the image signal Pin is displayed on a screen provided at a front portion of the CRT 91.
In the conventional device 150, however, the frequency characteristic of the gain for the image signal Pc is fixed. That is, the frequency characteristic disadvantageously can not be freely varied depending on a type of the image or the like. Another type of the conventional device 150 is known in which the resistor 95 is replaced with a pre-set variable resistor. In this type, the resistance of the pre-set variable resistor, however, can not be varied with electric means. Therefore, it is disadvantageously hard to adjust the frequency characteristic in order to optimize the visual image quality depending on the type of the image.
Further, a technique is not known which allows control of the frequency characteristic and the like exclusively for a particular region within entire one frame image where the particular type of the image is laid out so that the image quality in the region is suited to the type of the image. Thus, the conventional device is disadvantageous in that it is hard to obtain the optimum image quality depending on the type of the image.
The following documents are known in relation to the control of the frequency characteristic of the video amplifying circuit: Japanese Patent Laid Open Gazette No. 50-68221, No. 2-312465, and No. 6-189161.
A first aspect of the present invention is directed to an image display device. The image display device comprises: an image output unit for displaying an image represented by an image signal; an amplifying unit for amplifying the image signal with a gain having a frequency characteristic and supplying the amplified image signal to the image output unit, including a variable inductor, an inductance of which defines the frequency characteristics; and a control unit for controlling the inductance of the variable inductor.
According to a second aspect of the present invention, in the image display device of the first aspect, the amplifying unit further comprises an amplifier for amplifying the image signal, and the variable inductor is interposed into a path between the amplifier and the image output unit.
According to a third aspect of the present invention, in the image display device of the first or the second aspect, the variable inductor includes primary and secondary windings inductively coupled with each other, the primary winding is connected to the amplifier, the secondary winding is connected to the control unit, the inductance of the variable inductor is an inductance of the primary winding, and the control unit controls a current which is induced in the secondary winding by a current flowing in the primary winding.
According to a fourth aspect of the present invention, in the image display device of any one of the first to the third aspects, the image display device receives a synchronizing signal of the image, and further comprises a resolution detection unit for detecting a resolution of the image signal on a basis of the synchronizing signal, and the control unit varies the frequency characteristic depending on the resolution.
According to a fifth aspect of the present invention, in the image display device of any one of the first to the fourth aspects, the image display device further comprises a transient characteristic detection unit for detecting a pulse waveform of the image signal outputted from the amplifying unit, and the control unit controls the frequency characteristic so that the pulse waveform detected by the transient characteristic detection unit approaches a target form.
According to a sixth aspect of the present invention, in the image display device of any one of the first to the fifth aspects, the image display device further comprises a brightness detection unit for detecting a brightness of the image displayed by the image output unit, and the control unit judges the display image on a basis of the brightness as a binary image of normal display or a binary image of reverse display and controls the frequency characteristic as to enhance a higher frequency component of the gain for the binary image of normal display and to reduce the higher frequency component for the binary image of reverse display.
A seventh aspect of the present invention is directed to an image display device. The image display device comprises: an image output unit for displaying an overall image represented by an image signal; a region designation unit  less than 8 greater than  for designating a particular region  less than W greater than  within the overall image; and a control unit  less than 4 greater than  for selectively controlling an image quality of an image for the particular region.
According to an eighth aspect of the present invention, in the image display device of the seventh aspect, the image display device receives a synchronizing signal on which a position signal is superimposed and the region designation unit comprises: a position signal extraction unit for extracting the position signal from the synchronizing signal, and a region decision unit for deciding the particular region on a basis of the position signal.
According to a ninth aspect of the present invention, in the image display device of the seventh aspect, the image display device receives the image signal together with a position signal which is superimposed on the image signal, and the region designation unit comprises: a position signal extraction unit for extracting the position signal superimposed from the image signal, and a region decision unit for deciding the particular region on a basis of the position signal.
According to a tenth aspect of the present invention, in the image display device of the eighth or the ninth aspect, the position signal represents a type of the image quality to be controlled, the region designation unit further comprises an image quality control decoding unit for decoding the position signal into the type of the image quality, and the control unit selectively controls the type of the image quality based on the image quality.
In the device of the first aspect, since the frequency characteristic of the gain of the amplifying unit is controlled by controlling the inductance of the variable inductor, the frequency characteristic can be easily and electrically adjusted so as to be suited for the image signal and thereby a visually desirable image quality can be obtained.
In the device of the second aspect, since a variable inductor is interposed into a path between the amplifier and the image output unit, the amplifying unit is obtained by replacing an inductor provided in a conventional device with the variable inductor. Therefore, design and manufacturing sources such as design data in the conventional device can be used as they are, which reduces design and manufacturing cost.
In the device of the third aspect, the variable inductor includes primary and secondary windings inductively coupled with each other, and the inductance of the primary winding is controlled by controlling the current flowing in the secondary winding. Hence, the electrical control of the frequency characteristic can be further easily performed.
In the device of the fourth aspect, since the frequency characteristic is so controlled as to change depending on the resolution of the image signal, the frequency characteristic visually suitable for the resolution of the image signal can be obtained automatically.
In the device of the fifth aspect, the frequency characteristic is so controlled that the pulse waveform of the image signal supplied to the image output unit approaches a target form. Therefore, visually proper frequency characteristic is automatically obtained irrespective of the pulse waveform of the inputted image signal.
In the device of the sixth aspect, the frequency characteristic is properly changed according to the display type i.e. the normal or reverse display of the image displayed by the image output unit when the image is a binary image. Therefore, the image having visually desirable image quality can be automatically displayed even if the display type changes.
In the device of the seventh aspect, the image quality is selectively controlled for a particular region designated within the overall image. Therefore, it is possible to control the image quality e.g. frequency characteristic or brightness selectively for a particular image among plural images included in the overall image so that the image quality is suited to the type of the image.
In the device of the eighth aspect, the particular region is decided on the basis of the position signal superimposed on the synchronizing signal inputted together with the image signal from the exterior. Therefore, the region can be designated by an external device which supplies the image signal to the image display device.
In the device of the ninth aspect, the particular region is decided on the basis of the position signal superimposed on the image signal inputted from the exterior. Therefore, the particular region can be designated by an external device which supplies the image signal to the image display device. Moreover, the position signal is displayed on a screen of the image output unit because of being superimposed on the image signal. Hence, it is easy to recognize the particular region visually.
In the device of the tenth aspect, the type of the image quality to be controlled e.g. the frequency characteristic or the brightness is decided on the basis of the position signal. Therefore, an external device can designate the type of image quality control to be performed for the particular region. Accordingly, it is possible to control the image quality flexibly so as to obtain visually desirable image quality for various types of images to be displayed.
Accordingly, it is an object of the present invention to obtain an image display device capable of optimizing visual quality of the image displayed on a screen depending on the type of the image.
These and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.